Method and apparatus for protecting digital data by double re-encryption

ABSTRACT

A method and an apparatus ensuring protection of digital data are provided. In addition to re-encrypting the data using an unchangeable key, the data is double re-encrypted using a changeable key. The changeable key is used first and the unchangeable key is then used, or in another case, the unchangeable key is used first, and the changeable key is then used. In the aspect of embodiments, there is a case adopting a software, a case adopting a hardware, or a case adopting the software and the hardware in combination. The hardware using the unchangeable key developed for digital video is available. In adopting the software, encryption/decryption is performed in a region below the kernel which cannot be handled by the user to ensure the security for the program and for the key used. More concretely, encryption/decryption is performed with RTOS using a HAL and a device driver, i.e., a filter driver, a disk driver and a network driver, in an I/O manager. Either one of two filter drivers, with a file system driver between them, may be used. Further, both filter drivers may be used.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a Continuation of prior U.S. application Ser. No.09/806,510, filed Apr. 16, 2001 titled “METHOD AND APPARATUS FORPROTECTING DIGITAL DATA BY DOUBLE RE-ENCRYPTION” by Makoto Saito.

The present invention relates to a system for managing digital contents.In particular, the present invention relates to a system used formanaging copyrights of digital content, for which copyrights areclaimed, and for protecting the secrecy of the digital content so as toachieve enhanced digital content distribution and to realize digitalcontent commerce.

PRIOR ART

Hitherto, widely spread analog content deteriorate in quality each timeit is stored, copied, edited and transferred. Hence, no seriousdetriment from copyright violations occurs during these operations.However, digital content does not deteriorate in quality after repeatedstoring, coping, editing and transferring. Thus, the control of digitalcontent copyright is an important issue.

Digital data such as digital video data, digital audio data, etc. isusually supplied to users on a payment basis accompanying a broadcast,transfer of a DVD, etc. In these cases, the data is encrypted andsupplied in a manner which excludes unpaid viewing. The encrypted andsupplied digital data is decrypted using a crypt key, which is suppliedto the user by certain means, before the data is viewed. Because thequality of decrypted digital data does not deteriorate even when it isstored, copied or transferred, if the data is stored, copied ortransferred by the user, secondary viewing free of charge may occur.Non-authorized re-use of the decrypted digital data content is againstthe benefit of the data content provider. In this respect, systems andequipment have been developed to prohibit re-use, i.e., secondaryutilization such as storage, copying or transferring the digital datacontent.

However, the prohibition of the secondary utilization makes it lessattractive for users of the digital data content and it is nowrecognized that this may hinder the propagation of the use of thedigital data content. In this respect, it is now proposed to preventillegitimate use by re-encrypting the decrypted digital data content sothat the use of the digital data content is more attractive for users.

When the digital data, which is stored in a medium and is given or lentto a user or which is transferred to the user, is used for secondaryutilization such as storing, copying or transferring, it is impossiblefor the copyright owner to protect his or her copyright(s) in thedigital data, which is in the hands of the users. Therefore, a certainmethod is required to protect copyrights automatically and forcibly.

Under such circumstances, the present inventor has made variousproposals with the purpose of protecting digital content copyrights.

In Japanese Patent Laid-Open Publications 46419/1994 (GB-2269302; U.S.Ser. No. 08/098,415) and 141004/1994 (U.S. Pat. No. 5,794,115; U.S. Pat.No. 5,901,339), the present inventor proposed a system for managingcopyrights by obtaining a permit key from a key control center via apublic telephone line, and also, an apparatus for such a purpose inJapanese Patent Laid-Open Publication 132916/1994 (GB-2272822; U.S. Ser.No. 08/135,634).

Also, in Japanese Patent Laid-Open Publications 271865/1995(EP0677949A2; U.S. Ser. Nos. 08/416,037) and 185448/1996 (EP0704785A2;U.S. Ser. No. 08/536,747), a system for copyright management of thedigital contents was proposed.

In these systems and apparatus, those who wish to view an encryptedprogram makes a viewing request to a management center via acommunication line using a communication device. Upon receipt of theviewing request, the management center transmits a permit key andcharges and collects a fee.

Upon receipt of the permit key, the requestor transmits the permit keyto a receiving device by on-line or off-line means. When the permit keyis received, the receiving device decrypts the encrypted program byusing the permit key.

The system described in Japanese Patent Laid-Open Publication271865/1995 (EP0677949A2; U.S. Ser. No. 08/416,037), uses a program formanaging the copyright and copyright information, in addition the keyfor use permission, to manage the copyright of the digital content indisplaying (including process to sound), storing, copying, editing andtransferring the digital contents, including real-time transmission ofdigital video content, in a database system. The program for copyrightmanagement watches and manages in a manner that the digital content isnot used outside the use permission or user's request.

Japanese Patent Laid-Open Publication 271865/1995 (EP0677949A2; U.S.Ser. No. 08/416,037) describes that the digital content is supplied froma database in the encrypted state and is decrypted by the copyrightmanagement program only when it is displayed or edited, and is again inthe encrypted state when it is stored, copied or transferred. Further,it describes that the copyright management program itself is encryptedand is decrypted by using a permit key, and the decrypted copyrightmanagement program performs decryption and encryption of the copyrighteddata, and that, when a utilization other than storing and displaying thedata is performed, copyright information including information of theperson who performed the utilization is added to the original copyrightinformation and stored as history.

Japanese Patent Laid-Open Publication 287014/1996 (U.S. Pat. No.5,867,579; EP0715241A-2) proposed an apparatus fordecryption/re-encryption having a configuration of a board, a PCMCIAcard, an IC card or an IC for the copyright management and a crypt keyescrow system. This application also describes the copyright, managementmethod applied to a video conference system and an electronic commercesystem. U.S. Pat. No. 5,805,706, also describes an apparatus fordecryption/re-encryption having an IC configuration.

Japanese Patent Laid-Open Publication 272745/1996 (U.S. Pat. No.5,646,999; EP0709760) proposed a system, in which the copyright oforiginal data and the copyright of new data produced by editing theoriginal data or editing a plurality of original data are protected byconfirming the validity of a use request based on a digital signature onan edit program, in combination with the use of a secret-keycryptosystem and a public-key cryptosystem.

Japanese Patent Laid-Open Publication 288940/1996 (U.S. Pat. No.5,740,246; EP0719045A2) proposed various forms for applying thecopyright management system to a database system, a video-on-demand(VOD) system or an electronic commerce system.

Japanese Patent Laid-Open Publication 288940/1996 (U.S. Pat. No.5,848,158; EP0746126A2) proposed a system in which copyrights oforiginal data and new data are protected by using a third crypt key anda copyright label in case of using and editing a plurality of data.

As it can be understood from the data copyright management systems andthe data copyright management apparatus proposed by the present inventoras described above, the management of data copyrights can beaccomplished by encryption/decryption/re-encryption and limiting usageof digital content by the copyright management program. The cryptographytechnique and usage limitation can be realized by using a computer.

In a case where secret information is exchanged via a network, theinformation is encrypted for preventing piracy.

It is described in U.S. Pat. No. 5,504,818 and U.S. Pat. No. 5,515,441that information piracy during transmission is prevented by encryption.Using a plurality of keys in such a case is described in U.S. Pat. Nos.5,504,116, 5,353,351, 5,475,757 and 5,381,480, and performingre-encryption is described in U.S. Pat. No. 5,479,514.

The protection of copyrights in the secondary utilization of digitaldata by the copyright management program can be realized byre-encryption/re-decryption of the decrypted digital data and bymanaging and performing the re-encryption/re-decryption by using thecopyright management program.

Of course, it goes without saying that the means for carrying outre-encryption/re-decryption includes cases where software is used andcases where hardware is used.

Here, the operation to obtain encrypted data C from non-encrypted data Mby using a key K is expressed as:C=E(M, K).and to obtain decrypted data M from encrypted data C by using the key Kis expressed as:M=D(C, K).

When re-encryption/re-decryption of the decrypted data M is repeated,re-encryption is expressed as:∀i:Ci=E(D(Ci-1, Ki-1), Ki),where i is a positive integer, and re-decryption is expressed as:∃:M=D(E(Ci-1, Ki-1), Ki).

Referring to FIG. 1, description will be given on an arrangement of aconventional set-top box (STB) and on a method for protecting thedigital data performed in the set-top box.

Description is not given here on peripheral circuits not directlyrelated to encryption/decryption, e.g., the description for an amplifierunit and a compression/expansion unit is omitted.

FIG. 1, reference numeral 1 represents digital data supplied bybroadcasting means such as digital terrestrial wave broadcasting,digital CATV broadcasting, digital satellite broadcasting, etc., bynetwork means such as the Internet, or by a digital storage medium suchas a DVD, a CD, etc. The data is encrypted by using a first changeablekey K1 to prevent illegitimate use:C1=E(M, K1)and is supplied to a set-top box 2.

When the encrypted digital data C1 is supplied to the set-top box 2, theencrypted digital data C1 is decrypted by a decryption unit 3 using thefirst changeable key K1 obtained from a key center via the same route asor via a different route from that of the encrypted digital data C1:M=D(C1, K1)and data M thus decrypted is outputted to a display unit 4 or the like.

In a case where the decrypted data M is stored in a medium such as adigital versatile disk (DVD) RAM or a hard disk, etc., or it istransferred externally via a network, the decrypted data M isre-encrypted by an encryption unit 6 within an unchangeable keyencryption/decryption unit 5, using an unchangeable key K0:$\begin{matrix}{{\forall{0\text{:}C\quad 0}} = {E\left( {M,{K\quad 0}} \right)}} \\{= {E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 0}} \right)}}\end{matrix}$and re-encrypted data C0 is stored in or transferred to an externaldevice 8.

In a case where the re-encrypted data C0 is used again, the re-encrypteddata C0 read from a storage medium of the external device 8 ortransferred via the network is re-decrypted using the unchangeable keyK0 by a decryption unit 7 of the unchangeable key encryption/decryptionunit 5: $\begin{matrix}{{\exists{\text{:}M}} = {D\left( {{C\quad 0},{K\quad 0}} \right)}} \\{= {D\left( {E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 0}} \right)} \right.}}\end{matrix}$and the decrypted data M is outputted to the display unit 4 or the like.

In this case, in order to ensure security, it may be arranged in such amanner, that the re-encrypted data C0 in the storage medium is erasedwhen the re-encrypted data C0 is read from the storage medium via aroute shown by a broken line in the figure and that the datare-encrypted again by using the unchangeable key K0 is re-stored.

In U.S. Pat. No. 5,805,706, an integrated circuit for performingre-encryption/re-decryption is described.

In the set-top box as arranged above it is easy to handle becausere-encryption/re-decryption is automatically carried out by the hardwareby using the unchangeable key K0, and it is effective for forciblere-encryption/re-decryption of the digital data, which must beprotected.

However, since the unchangeable key K0 is placed in the device, andsince there is the possibility that the unchangeable key K0 may be knownto others, it may become impossible to protect the digital datathereafter.

SUMMARY OF THE INVENTION

To solve the above problem, the present invention provides a method andan apparatus for double re-encrypting the data by using a changeable keyin addition to re-encrypting by using an unchangeable key.

In use of the unchangeable key and the changeable key, there are caseswhere the changeable key is used and an unchangeable key is then used,and where the unchangeable key is used first and the changeable key isthen used.

The key used first when re-encrypting is the final key used whendecrypting, and accordingly, even if data, which is subsequentlyre-encrypted, is cryptanalyzed,security,is highly ensured. Therefore, ina case where a changeable key is used first and an unchangeable key isnext used for re-encryption, the possibility that the changeable key isknown to others is very low even when the unchangeable key has beenknown to the others.

In the aspects of the embodiments of the present invention, softwareand/or hardware may be used. In an embodiment using hardware, hardwareusing the unchangeable key developed for digital video can be used.

In an embodiment using software, in order to ensure the security of theprogram and the key used, encryption/decryption is performed in a regionunder a kernel, which cannot be handled by users. More concretely,encryption/decryption is performed at a filter driver, a device driver,i.e., a disk/network driver, and a real-time OS using HAL in an I/Omanager. There are two filter drivers with a file system driverinterposed between them and either one of the filter drivers may beused, or both may be used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a general arrangement of a conventional set-top box;

FIG. 2 shows a general arrangement of a first embodiment of the presentinvention applied to a set-top box;

FIG. 3 shows a general arrangement of a second embodiment of the presentinvention applied to a set-top box;

FIG. 4 shows a general arrangement of a third embodiment applied to anapparatus using a personal computer;

FIG. 5 shows a general arrangement of a fourth embodiment applied to anapparatus using a personal computer;

FIG. 6 is a drawing to give detailed explanation for the fourthembodiment; and

FIG. 7 shows a general arrangement of a fifth embodiment applied to anapparatus using a personal computer.

FIG. 8 shows a general arrangement of a sixth embodiment set-top boxwhich is a variation of the first embodiment;

FIG. 9 shows a general arrangement of a seventh embodiment set-top,which is a variation of the sixth embodiment;

FIG. 10 shows a general arrangement of an eighth embodiment using apersonal computer;

FIG. 11 illustrates a detailed description on the eighth embodiment;

FIG. 12 illustrates an embodiment of a copyright management apparatus;

FIG. 13 illustrates another embodiment of the copyright managementapparatus; and

FIG. 14 illustrates still another embodiment of the copyright managementapparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following describes embodiments of the present invention.

Referring to FIG. 2, description will be given on an arrangement of aset-top box (STB) of a first embodiment of the present invention, and amethod for protecting the digital data in the set-top box.

In the set-top box of this embodiment, as with the conventional set-topbox example as shown in FIG. 1, description is not given on peripheralcircuits not directly related to encryption/decryption, e.g., anamplifier unit, a compression/expansion unit and an interface unit tothe outside.

The difference of the present embodiment from the conventionallyproposed set-top box shown in FIG. 1 is that a changeable keyencryption/decryption unit 19 for performing decryption using a secondchangeable key K2 is inserted between an unchangeable keyencryption/decryption unit 15 performing encryption/decryption by usingthe unchangeable key K0 and a decryption unit 13.

In FIG. 2, reference numeral 11 represents digital data supplied bybroadcasting means such as digital terrestrial wave broadcasting,digital CATV broadcasting, digital satellite broadcasting, etc., bynetwork means such as Internet, or by digital storage medium such as aDVD, a CD, etc. The digital data is encrypted by using a firstchangeable key K1 to prevent illegitimate use:C1=E(M, K1)and is supplied to a set-top box 12.

When the encrypted digital data C1 is supplied to the set-top box 12,the encrypted digital C1 is decrypted by the decryption unit 13 usingthe first changeable key K1 obtained from a key center vis the sameroute as or via a route different from that of the encrypted digitaldata C1:M=D(C1, K1)and the decrypted data M is outputted to a display unit 14 or the like.

In a case where the decrypted data M, for which copyrights are claimed,is stored in an external device 18, i.e., in a medium of a digitalversatile disk (DVD) RAM or a hard disk, or in a case where the data istransferred externally via a network, the decrypted data M isre-encrypted using a second changeable key K2 at an encryption unite 20of the changeable key encryption/decryption unit 19: $\begin{matrix}{{\forall{2\text{:}C\quad 2}} = {E\left( {M,{K\quad 2}} \right)}} \\{{= {E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 2}} \right)}},}\end{matrix}$further, the re-encrypted data C2 is double re-encrypted using anunchangeable key K0 by an encryption unit 16 of the unchangeable keyencryption/decryption unit 15: $\begin{matrix}{{\forall{2 - {0\text{:}C\quad 2} - 0}} = {E\left( {{C\quad 2},{K\quad 0}} \right)}} \\{{= {E\left( {{E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 2}} \right)},{K\quad 0}} \right)}},}\end{matrix}$and the double re-encrypted data C2-0 is stored in the external device18 or transferred.

In a case where the double re-encrypted data C2-0 is used again, there-encrypted data C2-0 read from the storage medium of the externaldevice 18 or transferred from the network is re-decrypted by adecryption unit 17 of the unchangeable key encryption/decryption unit 15using the unchangeable key K0: $\begin{matrix}{{\exists{2\text{:}C\quad 2}} = {E\left( {{{C\quad 2} - 0},{K\quad 0}} \right)}} \\{= {D\left( {{E\left( {{E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 2}} \right)},{K\quad 0}} \right)},} \right.}}\end{matrix}$further, the re-decrypted data C2 is decrypted using the secondchangeable key K2 by a decryption unit 21 of the changeable keyencryption/decryption unit 19: $\begin{matrix}{{\exists{\text{:}M}} = {{D\left( {{C\quad 2},{K\quad 2}} \right)}.}} \\{= {D\left( {{E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 2}} \right)},} \right.}}\end{matrix}$and the decrypted data M is outputted to the display unit 14 or thelike.

In this case, in order to ensure the security, it may be arranged insuch a manner that, when the re-encrypted data C2-0 is read from thestorage medium via a route shown by a broken line in the figure, there-encrypted data C2-0 in the storage medium is deleted and the datare-encrypted by using the changeable key K2 and the unchangeable key K0is re-stored.

As described above, because the re-encryption using the secondchangeable key K2 is performed before the re-encryption using theunchangeable key, even when the unchangeable key K0 is discovered byothers, since the data is also encrypted by using the second changeablekey K2, it is very difficult to cryptanalyze the encrypted data withoutfurther finding out the second changeable key K2.

Also, the second changeable key K2 is first used for re-encryption, andit is again used for re-decryption after the unchangeable key K0 is usedfor double re-encryption and re-decryption. Accordingly, the security ofthe second changeable key K2 is highly ensured, and because it is usedfirst, it strongly governs the encrypted data in the most effectivemanner.

In the description of the above embodiment, the encryption unit 20 andthe decryption unit 21 are contained in the changeable keyencryption/decryption unit 19 and the encryption unit 16 and thedecryption unit 17 are contained in the unchangeable keyencryption/decryption unit 15. Of course, it goes without saying thatthese units 16, 17, 20 and 21 may also be separately provided.

The operations as described above can be easily implemented by providinga computer arrangement having a CPU and a system-bus in the set-top box12.

Now, referring to FIG. 3, description will be given on anotherarrangement of the set-top box, which is a second embodiment of thepresent invention, and also, on a method for protecting the digital datacarried out in this set-top box.

In this second embodiment set-top box, as with the conventional set-topbox example shown in FIG. 1, description is not given on peripheralcircuits not directly related to encryption/decryption, e.g., anamplifier unit and a compression/expansion unit.

The difference of the second embodiment set-top box from the firstembodiment set-top box shown in FIG. 2 is that the positions areswitched between the unchangeable key encryption/decryption unit 35 forencryption/decryption using the unchangeable key K0 and the changeablekey encryption/decryption unit 39 for encryption/decryption using thesecond changeable key K2.

An unchangeable key encryption/decryption unit 35 forencryption/decryption using the unchangeable key K0 is connected to adecryption unit 33 and a display 34, and an external changeable keyencryption/decryption unit 39 for encryption/decryption using the secondchangeable key K2 is connected to an external device 38. The secondchangeable key K2 may be supplied from the outside or may be generatedin the set-top box.

In FIG. 3, reference numeral 31 represents digital data supplied bybroadcasting means such as digital terrestrial wave broadcasting,digital CATV broadcasting, digital satellite broadcasting, etc., bynetwork means such as Internet, or by a digital storage medium such as aDVD, a CD, etc. The data is encrypted by using a first changeable key K1to prevent illegitimate use:C1=E(M, K1)and is supplied to a set-top box 32.

When the encrypted digital data C1 is supplied to the set-top box 32,the encrypted digital data C1 is decrypted by the decryption unit 33using the first changeable key K1 obtained via the same route as or viaa route different from that of the encrypted digital data C1:M=D(C1, K1)and the decrypted data M is outputted to a display unit 34 or the like.

In a case where the decrypted data M, for which copyrights are claimed,is stored in an external device 38, i.e., in a medium such as a digitalversatile disk (DVD) RAM or a hard disk, etc., or is transferredexternally via a network, the decrypted data M is re-encrypted using theunchangeable key K0 at the encryption unit 36 of the unchangeable keyencryption/decryption unit 35: $\begin{matrix}{{\forall{0\text{:}C\quad 0}} = {E\left( {M,{K\quad{0/}}} \right)}} \\{{= {E\left( {{D\left( {{C/1},{K\quad 1}} \right)},{K\quad 0}} \right)}},}\end{matrix}$further, the re-encrypted data C0 is double re-encrypted at anencryption unit 40 of the changeable key encryption/decryption unit 39by using the second changeable key K2: $\begin{matrix}{{\forall{0 - {2\text{:}C\quad 0} - 2}} = {/{E\left( {{C\quad 0},{K\quad 2}} \right)}}} \\{{= {E\left( {{E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 0}} \right)},{K\quad 2}} \right)}},}\end{matrix}$and double re-encrypted data C0-2 is stored in the external device 38 ortransferred.

In a case where the double re-encrypted data C0-2 is used again, there-encrypted data C0-2 read from the storage medium of the externaldevice 38 or transferred from the network is re-decrypted using theexternal changeable key K2 by the re-decryption unit 43 of the externalchangeable key encryption/decryption unit 39: $\begin{matrix}{{\exists{\text{:}0\text{:}C\quad 0}} = {D\left( {{{C\quad 0} - 2},{K\quad 2}} \right)}} \\{= {D\left( {{E/\left( {{E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 0}} \right)},{K\quad 2}} \right)},} \right.}}\end{matrix}$further, the re-decrypted data C0 is again re-decrypted using theunchangeable key K0 by a decryption unit 37 of the unchangeable keyencryption/decryption unit 35: $\begin{matrix}{{\exists{\text{:}M}} = {D\left( {{{/C}\quad 0},{K\quad 0}} \right)}} \\{= {D\left( {/{E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 0}} \right)}} \right.}}\end{matrix}$and the decrypted data M is outputted to the display unit 34 or thelike.

In this case, in order to ensure the security, it may be arranged insuch a manner that, when the re-encrypted data C2-0 is read from thestorage medium via a route shown by a broken line in the figure, thedouble re-encrypted data C0-2 in the storage medium is erased and thedata re-encrypted by using the unchangeable key K0 and the externalchangeable key K2 is re-stored.

As described above, because the re-encryption is performed using theunchangeable key K0 before the re-encryption using the second changeablekey K2, even when the unchangeable key K0 is discovered by others, sincethe data is also encrypted by using the second changeable key K2, it isvery difficult to cryptanalyze the encrypted data without furtherfinding out the second changeable key K2.

In this arrangement, the changeable key encryption/decryption unit 39 issimply added to the unchangeable encryption/decryption unit 35 of theconventionally proposed set-top box shown in FIG. 1, and accordingly, aset-top box employing the present invention can be easily achieved.

In the description of this embodiment, the encryption unit 36 and thedecryption unit 37 are contained in the unchangeable keyencryption/decryption unit 35 and the encryption unit 40 and thedecryption unit 41 are contained in the changeable keyencryption/decryption unit 39. Of course, it goes without saying thatthese units 36, 37, 40 and 41 may also be separately provided.

The operation as described above can be easily implemented by providinga computer arrangement having a CPU and a system-bus in the set-top box32.

Digital data content is handled not only in the set-top box but also ina computer such as a personal computer.

Referring to FIG. 4 through FIG. 7, description will be given onembodiments of the present invention applied to an apparatus using apersonal computer.

Unlike the set-top box where all components are constituted of hardwareand are operated only by the hardware, a personal computer is anapparatus, which is operated by controlling the hardware incorporated inthe apparatus using software.

In order to efficiently operate the computer, a) operating system (OS)is used, which manages the overall operation of the computer.

A conventional operating system used in the personal computer comprisesa kernel for providing basic services such as memory management taskmanagement, interrupt handling and communication between processes, andan operating system service providing other services.

However, with the advances in computer developments, for example, thefunctional improvements of a microprocesor and the price decrease of RAMused as main memory, and also the user's demand for an increase of theperformance ability of computers, improvements in the functions of theoperation system to manage the overall computer operation has beenrequired. Accordingly, the scale of the operating systems has becomecomparatively larger than before.

Since such an enlarged operating system itself occupies a large amountof space in the hard disk where it is to be stored, the space to storeapplication programs or data needed by the user is liable to be ratherlimited, and that may lead to inconvenience for the user in using thecomputer.

To cope with such situations, newer operating systems are of designedwith user-dependent subsystem parts (such as an environmental subsystemfor performing emulation of the other operating systems and graphics,and a core subsystem such as a security subsystem) removed from akernel. Basic parts of an operating system consist of a HAL (hardwareabstraction layer) to absorb differences of hardware, micro-kernels toprovide a scheduling function, an interrupt function, an I/O managementfunction, etc., and a system service API (application programminginterface) interposed between the subsystem and the micro-kernel.

With the above arrangement, expandability of the operating systemneeding changes or additions of function is improved, and portabilty ofthe operating system corresponding to the intended purpose can be mademuch easier.

By the distributed arrangement of elements of the micro-kernel to aplurality of network computers, it is now possible to easily realize adistributed operating system.

Computers are used in computer peripheral units, various types ofcontrol units, communication devices, etc., in addition to personalcomputers typically represented by the desk-top type or notebook typepersonal computers. In such cases, unlike the operating system for ageneral-purpose personal computer, in which importance is put on theman-machine interface, a real-time operating system is adopted, in whichimportance is placed on speedy execution. An operating system,especially one for embedding, is suitable for each of these units anddevices.

Of course, the cost for development is increased when developing anoperating system specially tailored for different embedded devices. Forthis reason, it is recently proposed to use a general-purpose operatingsystem in the personal computer also for the embedded type real-timeoperating system. By arranging a program specific for the embedded typein a subsystem combined with a micro-kernel, it is now practical toobtain an embedded type real-time operating system.

Major functions of the operating system include task management such ascheduling or interrupt processing.

The task management has mainly two different types in the operatingsystem: single task type, which only performs one task processing at thesame time, and multi-task type for performing a plurality of taskprocessings at the same time. The multi-task type is divided into amulti-task type where changeover of the task depends upon the task to beprocessed, and a multi-task type not dependent upon the task to beprocessed.

Among these, the single task type allocates one process to an MPU sothat the MPU is not free until the process is completed. Anon-preemptive multi-task type allows the MPU to be allocated aplurality of processes by time division, so that process is not executedunless the process in execution gives the control back to the operatingsystem. A preemptive multi-task type interrupts the process in executionat a certain time interval, so that the control is forcibly transferredto the other process.

Therefore real-time multi-tasking can be achieved only by the preemptivetype.

The task management in the computer is carried out according to theprocess, which is a unit having system resources such as a memory, afile, etc., and the process is managed according to a thread, which is aunit to allocate CPU time with divided processes. In this case, thesystem resources are shared by all threads in the same process. Thismeans that there are more than one thread to share system resources inone process.

Each task to be processed by the multi-task type has a priorityspectrum, which is generally divided into 32 steps. The normal taskperforming no interrupt is classified into dynamic classes, which aredivided into 0-15 steps, and the task performing interrupt is classifiedto real-time classes to be divided into 16-31 steps.

Interrupt processing is executed using an interrupt enable time(normally 10 milliseconds) called a “time slice” unit. Ordinaryinterrupt is executed at 10 millisecond time slices.

Under such circumstances, a time slice has been recently proposed, inwhich an interrupt enable time called a “real-tine slice” is 100microseconds. If this real-time slice is used, it is possible to executean interrupt with priority over the conventional interrupt of 10milliseconds.

In a third embodiment shown in FIG. 4, changeable keyencryption/decryption processing by software and the management of acrypt key in the computer are carried out by a real-time OS provided inthe HAL.

In FIG. 4, reference numeral 51 represents an operating system in acomputer; 56 a display unit for displaying output from the computer; 57an unchangeable key encryption/decryption unit; and 58 a data storagemedium such as a digital versatile disk (DVD) RAM or a hard disk, or adata transfer system such as a network.

The operating system 51 comprises an operating system service 52 and asystem service API 53, which are user regions, and a kernel 54 and a HAL55, which are non-user regions. The system service API 53 is arrangedbetween the operating system service 52 and the kernel 54 and serves tomediate between the operating system service 52 and the kernel 54. TheHAL 55 is arranged at the lowermost layer of the operating system 51 andserves to absorb differences in the hardware for the software.

The operating system service 52 comprises an application 59, a subsystem60 and a security subsystem 61. The kernel 54 comprises a plurality ofmicro-kernels 62 and 64 and a kernel 63. The micro-kernel 62 has taskmanagement functions such as scheduling, interrupt, etc., and themicro-kernel 64 has an I/O management function.

The micro-kernel 64 having the I/O management function comprises an I/Omanagement 65, device drivers such as a disk driver 67 and a networkdriver 68, which are managed by the I/O manager, and a filter driver 66which is inserted when necessary between the I/O manager 65 and thedevice drivers such as the disk driver 67 and the network driver 68.

The changeable key encryption/decryption processing in the computer isexecuted by software. In case of the third embodiment, the changeablekey encryption/decryption processing is carried out by theaforementioned real-time OS (RTOS) with priority over other tasks in theHAL 55 in the operating system 51.

Similar to the first embodiment shown in FIG. 2, digital data suppliedby broadcasting means such as digital terrestrial wave broadcasting,digital CATV broadcasting, digital satellite broadcasting, etc., bynetwork means such as Internet, or by a digital storage medium such as aDVD, a CD, etc., is encrypted using a first changeable key K1 to preventillegitimate use:C1=E(M, K1)and is supplied. The supplied encrypted digital data C1 is decrypted bythe operating system service 52 using the first changeable key K1provided from the key center via the same route as or via a routedifferent from that of the encrypted digital date C1:M=D(C1, K1)and the decrypted data M is outputted to the display unit 56 or thelike.

In a case where the decrypted data M, for which copyrights are claimed,is stored in a medium such as a digital versatile disk (DVD) RAM or ahard disk, or where it is transferred externally via a network, thedecrypted data M is mandatory re-crypted by HAL 55 using a secondchangeable key K2: $\begin{matrix}{{\forall{2\text{:}\quad C\quad 2}} = {E\left( {M,{K\quad 2}} \right)}} \\{= {{E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 2}} \right)}.}}\end{matrix}$Further, the re-encrypted data C2 is double re-encrypted at theunchangeable key encryption/decryption unit 57 by using an unchangeablekey K0: $\begin{matrix}{{\forall{2 - {0\text{:}\quad C\quad 2} - 0}} = {E\left( {{C\quad 2},{K\quad 0}} \right)}} \\{{= {E\left( {{E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 2}} \right)},{K\quad 0}} \right)}},}\end{matrix}$and the double re-encrypted data C2-0 is stored in an external device ortransferred. The changeable key K2 may be provided from the outside ormay be generated in a set-top box.

When the double re-encrypted data C2-0 is utilized, the doublere-encrypted data C2-0 read from the storage medium or transferred viathe network is re-decrypted using the unchangeable key KO at theunchangeable key encryption/decryption unit 57: $\begin{matrix}{{\exists{2\text{:}\quad C\quad 2}} = {D\left( {{{C\quad 2} - 0},{K\quad 0}} \right)}} \\{= {D\left( {{E\left( {{E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 2}} \right)},{K\quad 0}} \right)}.} \right.}}\end{matrix}$Further, the re-decrypted data is decrypted using the second changeablekey K2 by the HAL 55 having the changeable key encryption/decryptionfunction: $\begin{matrix}{{\exists{\text{:}\quad M}} = {D\left( {{C\quad 2},{K\quad 2}} \right)}} \\{= {D\left( {{E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 2}} \right)},} \right.}}\end{matrix}$and the decrypted data M thus obtained is outputted to the display unit56 or the like.

The real-time OS is executed in priority over every other task. In thethird embodiment, the real-time OS is implemented by the HAL, being acontact point with the hardware in the operating system. Accordingly,the re-encryption of the digital data is performed in a reliable manner,and it is impossible for decrypted data M, as it is, to be stored intothe external device or to be transferred. Also, re-encryption isperformed using the second changeable key K2 before the re-encryptionusing the unchangeable key KO. As a result, even if the unchangeable keyKO is known, it is very difficult to cryptanalyze the encrypted data byfinding out the second changeable key K2, as the data is also encryptedby the second changeable key K2.

Because the second changeable key K2 is used first and is then usedafter the unchangeable key KO has been used, key security can beensured. Because the second changeable key K2 has been used first, itstrongly governs the encrypted data.

The above operations can be easily implemented by arranging theunchangeable key encryption/decryption unit 57 as a sub-computerstructure having a CPU and a system-bus.

In a fourth embodiment shown in FIG. 5, the changeable keyencryption/decryption is provided by software carried out at a filterdriver 66 placed in the I/O management micro-kernel 64 in the kernel 54.

FIG. 6 shows an arrangement of the I/O management micro-kernel 64 withthe filter driver placed in it.

In an I/O management micro-kernel with no filter driver placed in it, afile system driver 69, an intermediate driver 70 and a device driver 71are arranged from an upper hierarchy to a lower hierarchy. Whennecessary, a filter driver 66A or a filter driver 66B is placed abovethe file system driver 69 or between the intermediate driver 70 and thedevice driver 71.

Because the I/O management micro-kernel can be designed to have thesefilter drivers 66A and 66B perform re-encryption/re-decryption andmanagement of the key, the filter drivers 66A or 66B is designed tocarry out the re-encryption/re-decryption processing and the keymanagement in this embodiment.

The filter driver is arranged, not in the operating system service unit52 which can be handled by the user, but in the kernel 54 which cannotbe handled by the user. On the other hand, it is generally practiced tomake the specification change to fit the particular computer using theoperating system. In particular, it is not very rare to change the I/Omanager therein.

Utilizing the above, the modules having the function ofre-encryption/re-decryption processing and the key management are placedin the I/O manager as the filter driver 66A, or the filter-driver 66B inthe fourth embodiment.

Similar to the first embodiment shown in FIG. 2, digital data suppliedby broadcasting means such as digital terrestrial wave broadcasting,digital CATV broadcasting, digital satellite broadcasting, etc., bynetwork means such as Internet, or by digital storage medium such as aDVD, a CD, etc. is encrypted using a first changeable key K1 to preventillegitimate use:C1=E(M, K1)and it is supplied. The encrypted and supplied digital data C1 isdecrypted by the operating system service unit 52 using the firstchangeable key K1 provided from the key center via the same route as orvia a route different from that of the encrypted digital data C1:M=D(C1, K1)and the decrypted data M is outputted to the display unit 56 and thelike.

In a case where the decrypted data M, for which copyrights are claimed,is stored in a medium such as a digital versatile disk (DVD) RAM or ahard disk, or in a case where it is transferred externally via anetwork, the decrypted data M is mandatorily re-encrypted by the filterdriver 66A or 66B using the external changeable key K2:∀2:C2=E(M, K2)=E(D(C1, K1), K2).Further, the re-encrypted data C2 is double re-encrypted at the internalunchangeable key encryption/decryption unit 57, using an unchangeablekey K0: $\begin{matrix}{{\forall{2 - {0\text{:}\quad C\quad 2} - 0}} = {E\left( {{C\quad 2},{K\quad 0}} \right)}} \\{{= {E\left( {{E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 2}} \right)},{K\quad 0}} \right)}},}\end{matrix}$and double-re-encrypted data C2-0 is stored into the external device ortransferred. The changeable key K2 may be provided from the outside ormay be generated in a set-top box.

When the double re-encrypted data C2-0 is utilized again, the doublere-encrypted data C2-0 read from the storage medium or transferred viathe network is re-decrypted using the unchangeable key K0 at theinternal unchangeable key encryption/decryption unit 57: $\begin{matrix}{{\exists{2\text{:}\quad C\quad 2}} = {D\left( {{{C\quad 2} - 0},{K\quad 0}} \right)}} \\{= {D\left( {{E\left( {{E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 2}} \right)},{K\quad 0}} \right)}.} \right.}}\end{matrix}$Further, the re-decrypted data C2 is decrypted by the filter driver 66Aor 66B, using the second changeable key K2: $\begin{matrix}{{\exists{\text{:}M}} = {D\left( {{C\quad 2},{K\quad 2}} \right)}} \\{= {D\left( {E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 2}} \right)} \right.}}\end{matrix}$and the decrypted data M thus obtained is outputted to the display unit56 or the like.

The filter driver can be easily placed into the kernel of the operationsystem in a part of the A/O manager. In so doing, the function of there-encryption/re-decryption processing and the key management can beeasily incorporated into the operation system. Also, since re-encryptionis performed using the second changeable key K2 before the re-encryptionusing the unchangeable key K0, even if the unchangeable key K0 isdiscovered by others, it is very difficult to cryptanalyze the encrypteddata without finding out the second changeable key K2 because the datais also encrypted by the second changeable key K2.

Further, because the second changeable key K2 is used first, and isthen, used after the unchangeable key K0 is used, the key security canbe highly ensured. Also, because the second changeable key K2 is usedfirst, it strongly governs the encrypted data.

The above operations can be easily implemented by arranging theunchangeable key encryption/decryption unit 57 as a sub-computerstructure having a CPU and a system-bus.

In a fifth embodiment shown in FIG. 7, the changeable keyencryption/decryption and the key management is provided by softwarecarried out at the disk driver 67 and the network driver 68 contained inthe I/O management micro-kernel 64 in the operating system 51.

As already explained in connection with FIG. 6, the file system driver69, the intermediate driver 70, and the device driver 71 are arrangedfrom an upper hierarchy to a lower hierarchy in the I/O managementmicro-kernel. The changeable key encryption/decryption processing andthe key management can be carried out also in the device driver 71positioned at the lowermost layer.

Similar to the first embodiment shown in FIG. 2, the digital datasupplied by broadcasting means such as digital terrestrial wavebroadcasting, digital CATV broadcasting, digital satellite broadcasting,etc., by network means such as Internet, or by digital storage mediumsuch as a DVD, a CD, etc., is encrypted using the first changeable keyK1 to prevent illegitimate use:C1=E(M, K1)and it is supplied. The encrypted and supplied digital data C1 isdecrypted by the operating system service unit 52 using the firstchangeable key K1 provided from the key center via the same route as ora route different from that of the encrypted digital data C1:M=D(C1, K1)and the decrypted data M is outputted to the display unit 56 or thelike.

In a case where the decrypted data M, for which copyrights are claimed,is stored in a medium such as a digital versatile disk (DVD) RAM or ahard disk, or in a case where it is transferred externally via anetwork, the decrypted data M is mandatorily re-encrypted by the devicedriver 71, i.e., the disk driver 67 and the network driver 68, using thesecond changeable key K2: $\begin{matrix}{{\forall{2\text{:}\quad C\quad 2}} = {E\left( {M,{K\quad 2}} \right)}} \\{= {{E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 2}} \right)}.}}\end{matrix}$Further, the re-encrypted data C2 is double re-encrypted at theunchangeable key encryption/decryption unit 57 using the unchangeablekey K0 placed in the unchangeable key encryption/decryption unit 57:$\begin{matrix}{{{\forall{2 - 0}}:{{C\quad 2} - 0}} = {E\left( {{C\quad 2},{K\quad 0}} \right)}} \\{{= {E\left( {{E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 2}} \right)},{K\quad 0}} \right)}},}\end{matrix}$and double re-encrypted data C2-0 is stored in the external device ortransferred. The changeable key K2 may be provided from the outside ormay be generated in a set-top box.

When the double re-encrypted data C2-0 is utilized again, the doublere-encrypted data C2-0 read from the storage medium or transferred via anetwork is re-decrypted using the unchangeable key K0 by the internalunchangeable key encryption/decryption unit 57: $\begin{matrix}{{\exists{2\text{:}\quad C\quad 2}} = {D\left( {{{C\quad 2} - 0},{K\quad 0}} \right)}} \\{= {D\left( {{E\left( {{E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 2}} \right)},{K\quad 0}} \right)}.} \right.}}\end{matrix}$Further, the re-decrypted data C2 is decrypted by the device driver 71,i.e., the disk driver 67 and the network driver 68, using the secondchangeable key K2: ∃:M = D(C  2, K  2) = D(E(D(C  1, K  1), K  2)and the decrypted data M thus obtained is outputted to the display unit56 or the like.

For the device driver, it is generally practiced to make thespecification change to fit the particular computer using the operatingsystem or when the corresponding device has been modified.

Since the function of the re-encryption/re-decryption processing and thekey management is incorporated into such a device driver, it allows theeasy incorporation of the function into the kernel of the operatingsystem. Also, since re-encryption is performed using the secondchangeable key K2 before the re-encryption using the unchangeable keyK0, even if the unchangeable key K0 is discovered by others, it is verydifficult to cryptanalyze the encrypted data without finding out thesecond changeable key K2 because the data is also encrypted using thesecond changeable key K2.

There is a possibility that the second changeable key K2 may bediscovered by others, when it is repeatedly used. In such a case, it ispreferably designed in such a manner that the second changeable key K2used for encryption is abandoned and generated again when necessary fordecryption, as described in Japanese Patent Laid-Open Publication185448/1996 (EP0704885A2, U.S. Ser. No. 08/536,749). If it is necessaryto have the key for decryption, it should be obtained from the keycenter again.

For security purposes, K1, K2 and K0 may be based on different cryptalgorithms.

These operations can be easily implemented by arranging the unchangeablekey encryption/decryption unit 57 as a sub-computer structure having aCPU and a system bus.

In the embodiments described above, the second changeable key K2 and theunchangeable key K0 are used in addition to the first changeable key K1.In the embodiments described below, a third changeable key K3 is usedadditionally so that more reliable copyright, management of digitalcontent is provided.

Referring to FIG. 8, description will be given on an arrangement of aset-top box in a sixth embodiment of the present invention, which is avariation of the first embodiment, and also on a method for protectingdigital data carried out in the set-top box.

In the set-top box of this embodiment similar to the set top box of thefirst embodiment, no description is given on peripheral circuits notdirectly related to encryption/decryption, e.g., an amplifier unit and acompression/decompression unit.

The set-top box of the sixth embodiment has a difference from that ofthe first embodiment in distinguishing between a case where thedecrypted data M is stored in a storage medium 81 such as a hard disk,which is incorporated in or dedicated to the set-top box, and anothercase where the decrypted data M is stored in a removable medium, e.g., aDVD-RAM, in an external 82 or is transferred externally via a network.

The internal unchangeable key encryption/decryption unit 15 and furthera changeable key encryption unit 80 are provided. In a case where thedecrypted copyrighted data is stored, for example, in a hard disk as astorage medium 81, which is incorporated in or dedicated to the set-topbox, it is double re-encrypted using an internal unchangeable key K0. Onthe other hand, in a case where it is stored in a removable medium,i.e., a DVD-RAM, or is transferred externally via the network, it isdouble re-encrypted, not by the internal unchangeable key K0 but by athird changeable key K3.

In FIG. 8, reference numeral 11 represents digital data, which issupplied by broadcasting means such as digital terrestrial wavebroadcasting, digital CATV broadcasting, digital satellite broadcasting,etc., by network means such as Internet, or by a digital storage mediumsuch as a DVD, a CD, etc. The digital data is encrypted using a firstchangeable key K1 to prevent illegitimate use:C1=E(M, K1)and encrypted digital data C1 is supplied to a set-top box 12.

When the encrypted digital data C1 is supplied to the set-top box 12,the encrypted digital data C1 is decrypted by a decryption unit 13 usinga first changeable key K1 obtained from a key center:M=D(C1, K1)and the decrypted data M is outputted to a display unit 14 or the like.

In a case where the decrypted copyrighted data M is stored in a storagemedium 81 such as a hard disk, which is incorporated in or is dedicatedto the set-top box 12, or in a removable medium such as a DVD-RAM, orwhere it is transferred externally via a network, the decrypted data Mis re-encrypted by an encryption unit 20 of a changeable keyencryption/decryption unit 19 using a second changeable key K2, which isobtained from the key center or generated in the set-top box 12:∀2:C  2 = E(M, K  2) = E(D(C  1, K  1,), K  2).

In a case where the re-encrypted data C2 is stored in a hard disk of thestorage medium 81 incorporated into or dedicated to the set-top box 12,the re-encrypted data C2 is double re-encrypted by an encryption unit 16of an internal unchangeable key encryption/decryption unit 15 using anunchangeable crypt key K0 placed in the internal unchangeable keyencryption/decryption unit 15:∀2 − 0:C  2 − 0 = E(C  2, K  0) = E(E(D(C  1, K  1), K  2), K  0)and the double re-encrypted data C2-0 is stored in the storage medium 81or the like.

When the re-encryption data C2-0 stored in the storage medium 81 isutilized, the double re-encryption data C2-0 read from the storagemedium 81 is decrypted using the unchangeable crypt key K0 placed in adecryption unit 17 of the internal unchangeable keyencryption/decryption unit 15: $\begin{matrix}{{\exists{2\text{:}C\quad 2}} = {D\left( {{{C\quad 2} - 0},{K\quad 0}} \right)}} \\{= {D\left( {E\left( {{E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 2}} \right)},{K\quad 0}} \right)} \right.}} \\{= {E\left( {{E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 2}} \right)},} \right.}}\end{matrix}$further, the re-decrypted data C2 is decrypted using the changeable keyK2 by a decryption unit 21 of the changeable key encryption/decryptionunit 19: ∃:M = D(C  2, K  2) = D(E(D(C  1, K  1), K  2)and the decrypted data M is outputted to the display unit 14 or thelike.

In this case, in order to ensure security, when the double re-encrypteddata C2-0 is read from the storage medium 81 via a path shown by abroken line in the figure, it may be designed in a manner that thedouble re-encrypted data C2-0 in the storage medium 81 is erased at thattime, and that the data re-encrypted using the changeable key K2 and theinternal unchangeable key K0 is stored again.

In a case where the re-encrypted data C2 is stored in a DVD-RAM of aremovable medium, or it is transferred externally via a network at theexternals 82, the re-encrypted data C2 is double re-encrypted using athird changeable key K3, which is obtained from the key center orgenerated in the set-top box 12, by a changeable key encryption unit 80:∀2 − 3:C  2 − 3 = E(C  2, K  3) = E(E(M, K  2), K  3).

When the double re-encrypted data C2-3 sent to the externals 82 isutilized, the double re-encrypted data C2-3 is decrypted using the thirdchangeable key K3 stored at a decryption unit 84 of a changeable keyencryption/decryption unit 83:∃2:C  2 = D(C  2 − 3, K  3) = E(E(M, K  2), K  3), K  3) = E(M, K  2),further, the re-encrypted data C2 thus obtained is decrypted using thesecond changeable key K2 by a decryption unit 85 of the changeable keyencryption/decryption unit 83: ∃:M = D(C  2, K  2) = D(E(M, K  2), K  2)and the decrypted data M thus obtained is outputted to a display unit 86or the like.

These operations can be easily achieved by providing a sub-computerarrangement having a CPU and a system-bus in the set-top box 12.

Referring to FIG. 9, description will be given on an arrangement of aset-top box of a seventh embodiment, which is a variation of the sixthembodiment, and also on a method for protecting digital data carried outin the set-top box.

In the set-top box of this embodiment again, similar to the set-top boxof the sixth embodiment no description is given on peripheral circuitsnot directly related to encryption/decryption, e.g., an amplifier unitand a compression/decompression unit.

The seventh embodiment set-top box is different from that of the sixthembodiment in that the inserted positions are exchanged between theunchangeable key encryption/decryption unit 15 for performingencryption/decryption using the the unchangeable key K0 and thechangeable key encryption/decryption unit 19 for performingencryption/decryption using the second changeable key K2, and in thatthere is further provided a changeable key encryption unit 87 forperforming encryption/decryption using the second changeable key K2 forthe case where the data is stored in a DVD-RAM of a removable medium oris transferred externally via a network at the external 82.

The digital data 11, which is supplied by broadcasting means such asdigital terrestrial wave broadcasting, digital CATV broadcasting,digital satellite broadcasting, etc., by network means such as Internet,or by a digital storage medium such as a DVD, a CD, etc., in encryptedusing a first changeable key K1 in order to prevent illegitimate use:C1=E(M, K1)and encrypted digital data C1 is supplied to the set-top box 12.

When the encrypted digital data C1 is supplied to the set-top box 12,the encrypted digital data C1 is decrypted by the decryption unit 13using the first changeable key K1 obtained from the key center:M=D(C1, K1)and the decrypted data M thus obtained is outputted to the display unit14 or the like.

In a case where the copyrighted and decrypted date M is stored in thestorage medium 81 such as a hard disk incorporated in or dedicated tothe set-top box 12, the decrypted data M is re-encrypted to re-encrypteddata C0 using the unchangeable crypt key K0 by the internal unchangeablekey encryption/decryption unit 15:∀0:C  0 = E(M, K  0) = E(D(C  1, K  1), K  0).

The re-encrypted data C0 is double re-encrypted by the encryption unit20 of the changeable key encryption/decryption unit 19 using the secondchangeable key K2 obtained from the key center or generated in theset-top box 12: ∀  0 − 2:C  0 − 2 = E(C  0, K  2) = E(E(M, K  0), K  2)and the double re-encrypted data C0-2 is stored in the storage medium 81or the like.

When the double re-encrypted data C0-2 stored in the storage medium 81is utilized, the double re-encrypted data C0-2 read from the storagemedium 81 is re-decrypted by the decryption unit 21 of the changeablekey encryption/decryption unit 19 using the second changeable key K2:$\begin{matrix}{{\exists\quad{0\text{:}C\quad 0}}\quad = \quad{D\left( {{C\quad 0\text{-}2},{K\quad 2}} \right)}} \\{\quad{{= \quad{D\left( {{E\left( {{C\quad 0},{K\quad 2}} \right)},{K\quad 2}} \right)}},}}\end{matrix}$further, the re-decrypted data C0 is re-decrypted again using theunchangeable key K0 at the decryption unit 37 of the unchangeable keyencryption/decryption unit 15: $\begin{matrix}{{\exists{\text{:}M}} = \quad{D\left( {{C\quad 0},{K\quad 0}} \right)}} \\{\quad{= \quad{D\left( {{E\left( {M,{K\quad 0}} \right)},{K\quad 0}} \right)}}}\end{matrix}$and the decrypted data M thus obtained is outputted to the display unit14 or the like.

In this case, in order to ensure security, when the double re-encrypteddata C0-2 is read from the storage medium 81 via a route shown by abroken line in the figure, it may be designed in a manner that thedouble re-encrypted data C0-2 in the storage medium 81 is erased at thattime, and that the data re-encrypted using the second changeable key K2and the unchangeable key K0 is stored again.

In a case where the decrypted data M is stored in a DVD-RAM of aremovable medium or is transferred outside via a network at the external82, the decrypted data M is re-encrypted to re-encrypted data C3 using athird changeable key K3 obtained from the key center or generated in theset-top box 12 by the changeable key encryption unit 80: $\begin{matrix}{{{\forall 3}:{C\quad 3}}\quad = \quad{E\left( {M,{K\quad 3}} \right)}} \\{\quad{= \quad{{E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 3}} \right)}.}}}\end{matrix}$

The re-encrypted data C3 is encrypted to double re-encrypted data C3-2by the changeable key encryption unit 87 using the second changeable keyK2 obtained from the key center or generated at the set-top box 12:$\begin{matrix}{{\forall{3\text{-}2\text{:}C\quad 3\text{-}2}} = {E\left( {{C\quad 3},{K\quad 2}} \right)}} \\{= {E\left( {{E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 3}} \right)},{K\quad 2}} \right)}}\end{matrix}$and the double re-encrypted data C3-2 is stored in the DVD-RAM or istransferred via a network in the externals 82.

When the double re-encrypted data C3-2 sent to the externals 82 isutilized, the double re-encrypted data C3-2 is decrypted using thesecond changeable key K2 by the decryption unit 84 of the changeable keyencryption/decryption unit 83: $\begin{matrix}{{\exists{3\text{:}C\quad 3}} = {D\left( {{C\quad 3\text{-}2},{K\quad 2}} \right)}} \\{{= {D\left( {{E\left( {{C\quad 3},{K\quad 2}} \right)},{K\quad 2}} \right)}},}\end{matrix}$Further, the re-encrypted data C3 thus obtained is decrypted using thethird changeable key K3 by the decryption unit 85 of the changeable keyencryption/decryption unit 83: $\begin{matrix}{{\exists{\text{:}M}} = {D\left( {{C\quad 3},{K\quad 3}} \right)}} \\{= {D\left( {{E\left( {M,{K\quad 3}} \right)},{K\quad 3}} \right)}}\end{matrix}$and the decrypted data M thus obtained is outputted to the display unit86 or the like.

In the above embodiment, the third changeable key K3 is used by thechangeable key encryption unit 80 and the second changeable key K2 isused by the changeable key encryption unit 87, while this may beperformed in reverse order.

Also, it may be designed in a manner that the encryption unit 20 of thechangeable key encryption/decryption unit 19 serves the function of thechangeable key encryption unit 87.

While description has been given on the above in the case where theencryption unit 16 and the decryption unit 17 are contained in theunchangeable key encryption/decryption unit 15 and the encryption unit20 and the decryption unit 21 are contained in the changeable keyencryption/decryption unit 19, it goes without saying that these units16, 17, 20 and 21 may be separately provide.

These operation s can be easily achieved by providing a sub-computerarrangement having a CPU and a system-bus in the set-top box 12.

Description will be given on a variation, which is applied to anembodiment using a personal computer.

The eighth embodiment shown in FIG. 10 is a variation of the fourthembodiment shown in FIG. 5. In the embodiment, detailed descriptioncommon to the fourth embodiment arrangement is not given here.

The eighth embodiment is different from the fourth embodiment indistinguishing between the cases where the decrypted data M is stored ina storage medium 81 such as a hard disk incorporated in or dedicated tothe computer, and where it is stored in a removeable medium 92 such as aDVD-RAM or is transferred externally via a network 93.

For this purpose, changeable key encryption units 90 and 91 are providedas hardware 88, in addition to the unchangeable keyencryption/decryption unit 89. In a case where the copyrighted anddecrypted data is stored in the hard disk 81 of the storage mediumincorporated in or dedicated to the computer, it is double re-encryptedand decrypted using the unchangeable key K0 by the encryption/decryptionunit 89 via a disk driver 67. In a case where the data is stored in theDVD-RAM 92 of the removable medium, it is double re-encrypted anddecrypted using the third changeable key K3 by the encryption/decryptionunit 90 via the disk driver 67. In a case where the data is transferredexternally via the network 93, it is double re-encrypted and decryptedusing the third changeable key K3 by the changeable keyencryption/decryption unit 91 via a network driver 68.

Similar to the first embodiment shown in FIG. 2, the digital datasupplied by broadcasting means such as digital terrestrial broadcasting,digital CATV broadcasting, digital satellite broadcasting, etc., bynetwork means such as Internet, or by a digital storage medium such as aDVD, a CD, etc. is encrypted using a first changeable key K3 to preventillegitimate use:C1=E(M, K1)and is supplied. The encrypted data C1 that supplied is decrypted by theoperating system service 52 using the first changeable key K1 providedfrom the key center via the same route as or a route different from thatof the encrypted digital data C1:M=D(C1, K1)and the decrypted data M is outputted to the display unit 56 or thelike.

In cases where the decrypted data M is stored in the storage medium 81incorporated in or dedicated to the computer, such as a hard disk, whereit is stored in a medium such as the DVD-RAM, and where it istransferred externally via a network, the decrypted data M isre-encrypted by a filter driver 66 using the second changeable key K2obtained from the key center or generated in the operating systemservice 52: $\begin{matrix}{{\forall{2\text{:}C\quad 2}} = {E\left( {M,{K\quad 2}} \right)}} \\{{= {E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 2}} \right)}},}\end{matrix}$

Further, when the re-encrypted data C2 is stored in a storage medium 81incorporated in or dedicated to a computer, the re-encrypted data C2 isdouble re-encrypted using an unchangeable key K0 by theencryption/decryption unit 89 in the hardware 88:∀2-0:C2-0=E(C2, K0)=E(E(C1, K1), K2), K0)and re-encrypted data C2-0 is stored in the hard disk 81 or the like.

In the case where the double re-encrypted data C2-0 stored in thestorage medium 81 is utilized, the double re-encrypted data C2-0 readfrom the storage medium 81 is re-decrypted using the unchangeable key K0by the encryption/decryption unit 89 in the hardware 88:∃2:C2=D E(C2-0, K0)=D(E(D(C1, K1), K2), K0)further, the re-decrypted data C2 is decrypted using the secondchangeable key K2 by the filter driver 66 having encryption/decryptionfunction:∃:M=D(C2, K2)=D(E(D(C1, K1), K2),and the decrypted data M is outputted by the operating system of thecomputer to the display unit 56 or the like to be utilized.

When the re-encrypted data C2 is stored in a DVD-RAM of the removablemedium, the re-encrypted data C2 is double re-encrypted using the thirdchangeable key K3 by the changeable key encryption/decryption unit 90 ofthe hardware.∀2-3:C2-3=E(C2, K3)=E(E(D(C1, K1), K2), K3)and double re-encrypted data C2-3 is stored in the removable medium, theDVD-RAM.

In a case where the double re-encrypted data C2-3 stored in theremovable medium 92 is utilized, the double re-encrypted data C2-3 readfrom the removable medium 92 is re-decrypted using the third changeablekey K3 obtained from the key center or generated in the operating systemservice 52 by the encryption/decryption unit 90 in the hardware:∃2: C2=E(C2-3, K3=D(E(D(C1, K1), K2), K3)further, the re-decrypted data C2 is decrypted using the secondchangeable key K2 by the filter driver 66 having encryption/decryptionfunction:∃:M=D(C2, K2)=D(E(D(C1, K1), K2)and the decrypted data M is outputted by the operating system of thecomputer to the display unit 56 or the like to be utilized.

When the re-encrypted data C2 is transferred externally via the network93, the re-encrypted data C2 is double re-encrypted using the secondchangeable key K2 by the encryption/decryption unit 91:∀2-3: C2-3=E(C2, K3)=E(E(D(C1, K1), K2), K3)and double re-encrypted data C2-3 is transferred externally via thenetwork 93.

In a case where the double re-encrypted data C2-3 transferred from theoutside via the network 88 is utilized, the encrypted re-encrypted dataC2-3 is re-decrypted using the third changeable key K3 by theencryption/decryption unit 91:∃2: C2=E(C2-3, K3)=D(E(E(D(C1, K1), K2) K3),further, the re-decrypted data C2 is decrypted using the secondchangeable key K2 by the filter driver 66 having encryption/decryptionfunction:∃: M=D(C2, K2)=D(E(D(C1, K1), K2)and the decrypted data M is outputted by the operating system of thecomputer to the display unit 56 or the like to be utilized.

When the re-encrypted data C2 is transferred outside via the network 93,the re-encrypted data C2 is double re-encrypted using the secondchangeable key K2 at the encryption/decryption unit 91:∀2-3: C2-3=E(C2, K3)=E(E(D(C1, K1),K2), K3)and double re-encrypted data C2-3 is transferred outside via the network93.

In a case where the double re-encrypted data C2-3 transferred from theoutside via the network 88 is utilized, the encrypted data C2-3 isre-decrypted using the third changeable key K3 at theencryption/decryption unit 91:∃2: C2=E(C2-3, K3)=D(E(E(D(C1, K1), K2) K3),further, the re-decrypted data C2 is decrypted using the secondchangeable key K2 at the filter driver 66 having encryption/decryptionfunction:∃:M=D(C2, K2)=D(E(D(C1, K1), K2)and the decrypted data M is outputted by the operating system of thecomputer to the display unit 56 or the like to be utilized.

In the above embodiment, in order to facilitate the explanation, it hasbeen described that the encryption/decryption unit 90 and 91 areseparate, but it goes without saying that these units may be a singleunit.

The encryption/decryption as described above is managed by real-time OS(RTOS) as already explained with priority over other tasks in the HAL 55in the operating system 51.

These operations can be easily achieved by designing the hardware 88 asthe sub-computer arrangement having a CPU and a system-bus.

FIG. 11 shows a concrete arrangement of the encryption/decryption usingthe I/O management micro-kernel 64 having the filter driver 66 whichserves as the changeable key encryption/decryption processing of theeighth embodiment.

In the I/O management micro-kernel 64, a file system driver 69, anintermediate driver 70, and device drivers, i.e., a disk driver 67 and anetwork driver 68, are arranged from an upper hierarchy to a lowerhierarchy. When necessary, a filter driver 66A or a filter driver 66Bfor performing changeable key encryption/decryption is inserted abovethe file system driver 69 or between the intermediate driver 70 and thedevice driver.

Because these filter drivers 66A and 66B can performre-encryption/de-decryption, it is designed to have the filter driver66A or 66B carry out the re-encryption/re-decryption processing and themanagement of crypt keys in this embodiment.

In cases where the copyrighted and decrypted data M is stored in astorage medium such as a hard disk, incorporated therein or dedicatedthereto, where it is stored in a removable medium such as a DVD-RAM orwhere it is transferred outside via a network, the decrypted data M isre-encrypted by the filter driver 66A or 66B using the second changeablekey K2 obtained from the key center or generated in the I/O managementmicro-kernel 64;∀2:C2=E(M, K2)=E(D(C1, K1), K2).

Further, in a case where the re-encrypted data C2 is stored in acomputer-incorporated or dedicated storage medium 81, the re-encrypteddata C2 is double re-encrypted using the unchangeable key K0 by theencryption/decryption unit 89 in the hardware 88:∀2-0:C2-0=B(C2, K0)=E(E(D(C1, K1), K2), K0)and double re-encrypted data C2-0 is stored in the hard disk 81 or thelike.

When the double re-encrypted data C2-0 stored in the storage medium 81is utilized, the double re-encrypted data C2-0 read from the storagemedium 81 is re-decrypted using the unchangeable key K0 by theencryption/decrypted unit 89 in the hardware 88:∃2:C2=D(C2-0, K0)=D(E(E(D(C1, K1), K2), K0),further, the re-decrypted data C2 is decrypted using the secondchangeable key K2 by the filter driver 66 having theencryption/decryption function:∃:M=D(C2, K2)=D(E(D(C1, K1), K2)and the decrypted data M is outputted by the operating system of thecomputer to the display unit 56 or the like to be utilized.

Also, in a case where the re-encrypted data C2 is stored in theremovable medium such as a DVD-RAM, the re-encrypted data C2 is doublere-encrypted using the third changeable key K3 obtained from the keycenter or generated in the I/O management micro-kernel 64, by theencryption/decryption unit 90 in the hardware 88:∀2-3:C2-3=E(C2, K3)=E(E(D(C1, K1), K2), K3)and double re-encrypted data C2-3 is stored in a removeable medium suchas the DVD-RAM.

When the double re-encrypted data C2-3 stored in the removable medium 92is utilized, the re-encrypted data C2-3 read from the removeable medium92 is re-decrypted using the third changeable key K3 by theencryption/decryption unit 90 in the hardware 88:∃2:C2=D(C2-3, K3)=D(E(E(D(C1, K1), K2), K3),further, the re-decrypted data C2 is decrypted using the secondchangeable key K2 by the filter driver 66 having encryption/decryptionfunction:∃:M=D(C2, K2)=D(E(D(C1, K1), K2)and the decrypted data M is outputted by the operating system of thecomputer to the display unit 56 or the like to be utilized.

Also, in a case where the re-encrypted data C2 is transferred externallyvia the network 93, the re-encrypted data C2 is double re-encryptedusing the second changeable key K2 by the encryption/decryption unit 91:∀2-3:C2-3=E(C2, K3)=E(E(D(C1, K1), K2), K3)and double re-encrypted data C2-3 is transferred externally via thenetwork 93.

When the double re-encrypted data C2-3 transferred from the outside viathe network 93 is utilized, the re-encryption data C2-3 is re-decryptedusing the third changeable key K3 by the encryption/decryption unit 91:∃2:C2=E(C2-3, K3)=D(E(E(D(C1, K1), K2), K3),further, the re-decrypted data C2 is decrypted using the secondchangeable key K2 by the filter driver 66 having encryption/decryptionfunction:∃:M=D(C2, K2)=D(E(D(C1, K1), K2)and the decrypted data M is outputted by the operating system of thecomputer to the display unit 56 or the like to be utilized.

It is generally practiced that the specification of the device driver ischanged to fit the particular computer using the operating system oraccording to the corresponding device modified.

By providing the device driver with the function for there-encryption/decryption processing and the management of a key, itallows the easy incorporation of the function into the kernel of theoperating system. Also, by re-encryption the data using the secondchangeable key K2 before it is re-encrypted using the unchangeable keyK0, it is very difficult to cryptanalyze the encrypted data, even if theunchangeable key is discovered by others, without finding out the secondchangeable key K2 because the data is also encrypted using the secondchangeable key K2.

Further, because the second changeable key K2 is used first and then, isused after the unchangeable key K0 is used, high security of the key isensured. Because the second changeable key K2 is used first, it alsostrongly governs the encrypted data.

However, when the second changeable key K2 is repeatedly used, there isa possibility it may be discovered by others. In such a case, it ispreferably designed in such a manner that the second changeable key K2used for encryption is abandoned and it is again obtained from the keycenter or generated, when necessary for decryption, a described inJapanese Patent Laid-Open Publication 185448/1996 (EP0704885A2, U.S.Ser. No 08/536,749).

For security purposes, K1, K2, K3, and K0 may be based on differentcrypt algorithms.

These operation can be easily implemented as a sub-computer structurehaving CPU and a system bus.

In order to perform re-encryption/re-decryption of digital data asabove, it is necessary to add, to the digital data, information toindicate that storage or transfer of the digital data is restricted. Ina case where the digital data is stored or transferred without beingedited, illegitimate use of the digital data can be prevented by themethod and the apparatus for re-encryption/re-decryption as describedabove.

However, when the digital data is edited, there is a possibility thatthe information to identify the restriction of storage or transfer maybe lost.

In such the case, it may be designed in a manner that all of the dataare re-encrypted/re-decrypted using a key specific to the device (amaster key).

In so doing, even the digital data which has been edited, for example,by the “cut & paste” method, can be prevented from illegitimate use byre-encryption/re-decryption.

Also, it may be designed in a manner that the digital data without theinformation to identify the restriction of storage or transfer only isre-encrypted/re-decrypted using the master key, and that the digitaldata provided with the information to identify the restriction ofstorage or transfer is re-encrypted/re-decrypted using the method andthe apparatus as explained in the above embodiments.

In a case where the copyrighted and encrypted digital data is utilizedin a specific device such as a set-top box, illegitimate storing,copying or transferring can be relatively easily prevented. Also, in acase where the copyrighted and encrypted digital data is utilized on acomputer, the management of storing, copying or transferring thedecrypted digital data can be executed by using thedecryption/re-encryption apparatus described in Japanese PatentLaid-Open Publication 287014/1996 (U.S. Pat. No. 5,867,579; EP0713241A2)or by using the decryption/re-encryption apparatus described in U.S.Pat. No. 5,805,706.

However, the digital data decrypted for the purpose of displaying orprinting is present on the bus of the computer, and it is possible tostore, copy or transfer the decrypted digital data via a deviceconnected to the bus. In the following, description will be given on acopyright management apparatus, which solves this problem.

FIG. 12 shows a structural example of a copyright management apparatus,in which a first changeable key and a second changeable key are used.

Also, this copyright management apparatus can be realized in aconfiguration such as a sub-board, a PCMCIA card, and IC card or an ICpackage for the purpose of security.

In FIG. 12, reference numeral 101 represents a CPU, A ROM 103, a RAM104, a hard disk drive 105, a flexible disk drive 106, a CD-ROM drive107, a modem 108, etc. are connected to a system-bus 102 connected tothe CPU 101.

Reference numeral 109 represents a copyright management apparatus, whichcomprises a decryption/encryption unit 110, a video interface 113, anaudio interface 114, and a printer interface 115.

A display unit 116, a speaker 117 and a printer 118 are connected to thevideo interface 113, the audio interface 114, and the printer interface115 respectively on the outer side of the computer.

The decryption/encryption unit 110 comprises a decryption unit 111 andan encryption unit 112.

The decryption unit 111 and the encryption unit 112 of thedecryption/encryption unit 110 are connected to the system bus 102 ofthe computer. The video interface 113, the audio interface 114, and theprinter interface 115 are connected to the decryption unit 111.

This arrangement can be easily achieved by designing the copyrightmanagement apparatus 109 as a sub-computer arrangement having a CPU anda system-bus.

In cases where the decrypted digital data M is stored in the hard diskdrive 105, where it is copied at the flexible disk drive 106 or where itis transferred via the modem 108, the decrypted digital data isre-encrypted using the second changeable key K2 by the encryption unit112: $\begin{matrix}{{\forall{2\text{:}C\quad 2}} = {E\left( {M,{K\quad 2}} \right)}} \\{{= {E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 2}} \right)}},}\end{matrix}$the re-encrypted digital data C2 is supplied to the system-bus 102, andis stored in the hard disk drive 105, copied in the flexible disk drive106 or transferred via the modem 108.

The encrypted digital data C1 encrypted using the first changeable keyK1 is supplied to the decryption unit 111 from the system-bus 102, andis decrypted using the first changeable key K1:M=D(C1, K1).

In a case where the decrypted digital data M is outputted to the displayunit 116 or the speaker 117, it is turned to analog at the videointerface 113 and the audio interface 114 in the copyright managementapparatus 109 and is outputted in a predetermined signal form.

When the decrypted digital data M is outputted to the printer 118, printdata is outputted via the printer interface 115.

When this copyright management apparatus 109 is used, the decrypteddigital data other than the data outputted to the printer is not presentoutside the copyright management apparatus 109. Because the dataoutputted to the printer is still data, digital data of a moving pictureor of audio data is not present outside the copyright managementapparatus 109.

In the computer, non-encrypted digital data is also present in additionto the decrypted digital data.

In order to process the non-encrypted digital data and the decrypteddata by distinguishing between them, it is necessary to provide a videointerface, an audio interface and a printer interface, and this wouldmake the system more complicated and costly. To avoid such situation, itmay be designed in a manner that non-encrypted digital data is processedat the video interface 113 and the audio interface 114 in the copyrightmanagement system 109.

FIG. 13 shows another arrangement example of a copyright managementapparatus, in which an unchangeable key is used in addition to the firstand the second changeable keys.

This copyright management apparatus can be realized in a configurationsuch as a sub-board, a PCMCIA card, an IC card, or an IC package forsecurity purpose.

In FIG. 13, reference numeral 101 represents a CPU, A ROM 103, a RAM104, a hard disk drive 105, a flexible disk drive 106, a CD-ROM drive107, a modem 108, etc. are connected to a system-bus 102 connected tothe CPU 101.

Reference numeral 120 represents a copyright management apparatus. Thecopyright management apparatus 320 has, in addition to thedecryption/encryption unit 110, an unchangeable key encryption unit 121,a crypt video interface 122, a crypt audio interface 123, and a cryptprinter interface 124.

The decryption/encryption unit 110 has a decryption unit 111 and anencryption unit 112.

Also, an encrypted digital video display unit 125, an encrypted digitalaudio player 126, and an encrypted digital data printer 127, whicharranged outside of the computer, are connected to the crypt videointerface 122, the crypt audio interface 123, and the crypt printerinterface 124.

The decryption unit 111 and the encryption unit 112 of thedecryption/encryption unit 110 are both connected to the computersystem-bus 102. The unchangeable key encryption unit 121 is furtherconnected to the decryption unit 111.

The crypt video interface 122, the crypt audio interface 123; and thecrypt printer interface 124 are connected to the unchangeable keyencryption unit 121.

The encrypted data display unit 125 is connected to the crypt videointerface 122, the encrypted audio data player 126 is connected to thecrypt audio interface 123 and the encrypted data printer 127 isconnected to the crypt printer interface 124.

The above arrangement can be easily realized by designing the copyrightmanagement apparatus 120 as a sub-computer arrangement having a CPU anda system-bus.

The encrypted data display, unit 125 has an unchangeable key decryptionunit 128 connected to the crypt video interface 122, a D/A converter 131connected to the unchangeable key decryption unit 128, and a displayunit 116 connected to the D/A converter 131.

The encrypted audio data player 126 has an unchangeable key decryptionunit 129 connected to the crypt audio interface 123, a D/A converter 132connected to the unchangeable key decryption unit 129, and a speaker 117connected to the D/A converter 132.

The encrypted data printer 127 has an unchangeable key decryption unit130 connected to the crypt interface 124 and a printer 118 connected tothe unchangeable key decryption unit 130.

Needless to say, the encrypted data display unit 125, the encryptedaudio data player 126 and the encrypted data printer 127 have othercomponents such as an amplifier.

The encrypted digital data C1 encrypted using the first changeable keyK1 is supplied to the decryption unit 111 from the system-bus 102, andit is decrypted using the first changeable key K1:M=D(C1, K1).

When the decrypted digital data M is stored at the hard disk drive 105or is copied at the flexible disk drive 106 or is transferred via themodem 108, it is re-encrypted using the second changeable key K2 by theencryption unit 112: $\begin{matrix}{\forall{= {2:{C\quad 2}}}} \\{= {E\left( {M,{K\quad 2}} \right)}} \\{{= {E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 2}} \right)}},}\end{matrix}$the re-encrypted digital data C2 is supplied to the system-bus 102, andit is stored at the hard disk drive 105, copied at the flexible diskdrive 106, or transferred via the modem 108.

When the decrypted digital data M is outputted to the encrypted datadisplay unit 125, the encrypted audio data player 126 or the encrypteddata printer 127, it is re-encrypted using the unchangeable key K0 bythe unchangeable key encryption unit 121 in the copyright managementapparatus 120: $\begin{matrix}{{\forall{0\text{:}C\quad 0}} = {E\left( {M,{K\quad 2}} \right)}} \\{= {/{{E\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 0}} \right)}.}}}\end{matrix}$

The re-encrypted digital data C0 is arranged to be provided to theencrypted data display unit 125, the encrypted audio data player 126 andthe encrypted data printer 127 at the crypt video interface 122, thecrypt audio interface 123 and the crypt printer interface 124respectively, and an encrypted display signal Cd0, and encrypted audiosignal Ca0 and an encrypted print signal Cp0 are respectively outputted.

When the encrypted display signal Cd0 is inputted to the encrypted datadisplay unit 125 from the crypt video interface 122, it is decryptedusing the unchangeable key K0 at the unchangeable key decryption unit128:Md=D(Cd0, K0),the decrypted display signal MA is converted to a displayable analogsignal by the D/A converter 131 and it is displayed on the display unit116.

If the display unit 116 is a digital display unit, which can display thedigital data as it is, the D/A converter 131 is unnecessary.

When the encrypted audio signal Ca0 is inputted to the encrypted audiodata player 126 from the crypt audio interface 123, it is decryptedusing the unchangeable key K0 by the unchangeable key decryption unit129:Ma=D(Ca0, K0),the decrypted audio signal Ma is converted to a playable analog signalby the D/A converter 132, and it is played by the speaker 117.

The encrypted print signal Cp0 inputted to the encrypted data printer127 from the crypt printer interface 124 is decrypted using theunchangeable key K0 by the unchangeable key decryption unit 130:Mp=D(Cp0, K0)and the decrypted print signal Mp is printed by the printer 118.

When this copyright management apparatus 120 is used, no decrypted datais present outside the copyright management apparatus 120.

As aforementioned, non-encrypted digital data is also present inaddition to the decrypted digital data in the computer.

In order to process the non-encrypted digital data and the decrypteddigital data by distinguishing between them, it is necessary to providea video interface, an audio interface and a printer interface, and thiswould make the system more complicated and costly. To avoid suchsituation, it may be designed in a manner that the non-encrypted digitaldata is processed by the unchangeable key re-encryption unit 121 of thecopyright management apparatus 120.

FIG. 14 shows another arrangement example of the copyright managementapparatus, in which an unchangeable key encryption unit is provided tofollow the video interface, the audio interface and the printerinterface.

The copyright management apparatus can be realized in a configurationsuch as a sub-board, a PCMCIA card, and IC card or an IC package forsecurity purpose.

In FIG. 14, reference numeral 101 represents a CPU. A ROM 103, a RAM104, a hard disk drive 105, a flexible disk drive 106, a CD-ROM drive107, a modem 108, etc., are connected to a system-bus 102 connected tothe CPU 101.

The copyright management apparatus can be realized in a configurationsuch as a sub-board, a PCMCIA card, an IC card or an IC package forsecurity purpose.

In FIG. 14, reference numeral 101 represents a CPU. A ROM 103, a RAM104, a hard disk drive 105, a flexible disk drive 105, a CD-ROM drive107, a modem 108, etc., are connected to a system-bus 102 connected tothe CPU 101.

Reference numeral 140 represents a copyright management apparatus, whichcomprises a decryption/encryption unit 110, a video interface 113, anaudio interface 114, a printer interface 141, and an unchangeable keyencryption unit 134.

The decryption/encryption unit 110 has a decryption unit 111 and anre-encryption unit 112.

The unchangeable key encryption unit 134 has an unchangeable keyencryption unit for video 135, an unchangeable key encryption unit foraudio 136, and an unchangeable key encryption unit for print 137. Theunchangeable key encryption units for video, audio, and print may bearranged in a single unit if it is available for sufficient encryptioncapacity.

The decryption unit 111 and the re-encryption unit 112 of thedecryption/encryption unit 110 are connected to the system-bus 102 ofthe computer. Further, the video interface 131, the audio interface 132and the printer interface 133 are connected to the decryption unit 111,and the unchangeable key encryption unit for video 135, the unchangeablekey encryption unit for audio 136 and the unchangeable key encryptionunit for print 137 are connected to these interfaces.

An encrypted digital video display unit 125, an encrypted digital audioplayer 126 and an encrypted digital data printer 127 arranged outsidethe computer are connected respectively to the unchargeable keyencryption unit for video 135, the unchangeable key encryption unit foraudio 163 and the unchangeable key encryption unit for print 137.

The above arrangement can be easily realized by designing the copyrightmanagement apparatus 140 as a sub-computer arrangement having a CPU anda system-bus.

The encrypted data display unit 125 has an unchangeable key decryptionunit 128 connected to the unchangeable key encryption unit for video135, a D/A converter 131 connected to the unchangeable key decryptionunit 128, and a display unit 116 connected to the D/A converter 131.

The encrypted audio data player 126 has an unchangeable key decryptionunit 129 connected to the unchangeable key encryption unit for audio136, a D/A converter 132 connected to the unchangeable key decryptionunit 129, and a speaker 117 connected to the D/A converter 132.

The encrypted data printer 127 has an unchangeable key decryption unit130 connected to the unchangeable key encryption unit for print 137 anda printer 118 connected to the unchangeable key decryption unit 130.

Needless to say, the encrypted data display unit 125, the encryptedaudio data player 126 and the encrypted data printer 127 have othercomponents such as an amplifier.

The encrypted digital data C1 encrypted using the first changeable keyK1 is supplied to the decryption unit 111 from the system-bus 102 and itis decrypted using the first changeable key K1:M=D(C1, K1).

When the decrypted digital data M is stored at the hard disk drive 105or copied at the flexible disk drive 106 or transferred via the modem108, it is re-encrypted using the second changeable key K2 by theencryption unit 112: $\begin{matrix}{{\forall{2\text{:}\quad C\quad 2}} = {B\left( {M,{K\quad 2}} \right)}} \\{{= {P\left( {{D\left( {{C\quad 1},{K\quad 1}} \right)},{K\quad 2}} \right)}},}\end{matrix}$the re-encrypted digital data C2 is supplied to the system-bus 102, andit is then stored at the hard disk drive 105, copied at the flexibledisk drive 106 or transferred via the modem 108.

When the decrypted digital data M is outputted to the encrypted datadisplay unit 125, the encrypted audio data player 126 or the encrypteddata printer 127, the decrypted digital data M is arranged to digitaldata Md, Ma and Mp to be provided to the display unit 116, the speaker117 and the printer 118 respectively at the video interface 131, theaudio interface 132 and the printer interface 133 in the copyrightmanagement apparatus 140. Then, these digital data are encrypted usingthe unchangeable key K0 by the unchangeable key encryption unit forvideo 135, the unchangeable key encryption unit for audio 136 and theunchangeable key encryption unit for print 137:Cd0=E(Md, K0)Ca0=E(Ma, K0)Cp0=E(Mp, K0)and the encrypted display signal Cd0, the encrypted audio signal Ca0 andthe encrypted print signal Cp0 are outputted.

The encrypted display signal Cd0 is imputted to the encrypted datadisplay unit 125 from the unchangeable key encryption unit for video135, and it is decrypted using the unchangeable key K0 at theunchangeable key decryption unit 128:Md=D(Cd0, K0).The decrypted display signal Md is converted to a displayable analogsignal at the D/A converter 131, and is displayed on the display unit116.

If the display unit 116 is a digital display unit, which can display thedigital data as it is, the D/A converter 131 is unnecessary.

The encrypted audio signal Ca0 is inputted to the encrypted audio dataplayer 126 from the unchangeable key encryption unit 136, and it isdecrypted using the unchangeable key K0 by the unchangeable keydecryption unit 129:Ma=D(Ca0, K0).The decrypted audio signal Ma is converted to a playable analog signalat the D/A converter 132, and is played at the speaker 116.

The encrypted print signal Cp0 is inputted to the encrypted data printer127 from the unchangeable key encryption unit 137, and it is decryptedusing the unchangeable key K0:Mp=D(Cp0, K0).The decrypted print signal Mp is printed by the printer 118.

When this copyright management apparatus 140 is used, no decrypted datais present outside the copyright management apparatus 140.

As aformentioned, non-encrypted digital data is also present in additionto the decrypted digital data in the computer.

In order to process the non-encrypted digital data and the decryptiondata by distinguishing between them, it is necessary to provide a videointerface, an audio interface and a printer interface, and this wouldmake the system more complicated and costly. To avoid such situation, itmay be disigned in a manner that the non-encrypted digital data isprocessed at the video interface 131, the audio interface 132 and theprinter interface 133 of the copyright management apparatus 140.

A secret-key cryptosystem is often used as a cryptosystem for encryptingdigital data. The most popular DES (Data Encryption Standard) in thesecret-key cryptosystem carries out encryption/decryption per 64-bitblock, unit of data. It is a typical block cipher method in thesecret-key cryptosystem and has been widely adopted. Using thisencryption/decryption per block processing allows the realization of amore high speed encryption/decryption processing.

In doing so, a plurality of encryption units and decryption units areprovided in the encryption/decryption unit. It allows these plurality ofencryption units and decryption units to be, in order, allocated theencryption/decryption processings of data blocks to be carried out. Andthen, encryption/decryption processing results, thus obtained, aresynthesized.

Further, it brings a supplemental effect that it is possible to use arespective crypt key for each data block and also to adopt a respectivecryptosystem for each data block. Then, more high security for digitaldata is possible.

1-178. (canceled)
 179. A method, comprising: encrypting digital datausing a changeable key and an unchangeable key to produce doubleencrypted digital data, wherein said unchangeable key is capable ofbeing operationally unchangeable at least during said encrypting of saiddigital data.
 180. The method according to claim 179, wherein saidencrypting digital data using said changeable key is done prior to saidencrypting digital data using said unchangeable key.
 181. The methodaccording to claim 179, wherein said encrypting digital data using saidunchangeable key is done prior to said encrypting digital data usingsaid changeable key.
 182. The method according to claim 179, whereinsaid encrypting of said digital data is done prior to storing, copyingand/or transferring said double encrypted digital data.
 183. The methodaccording to claim 182, wherein said encrypting of said digital dataprior to storing, copying and/or transferring said double encrypteddigital data is executed in priority over one or more other tasks toprevent non-encrypted digital data from being stored, copied and/ortransferred.
 184. An apparatus, comprising: means for encrypting digitaldata using a changeable key; and means for encrypting said digital datausing an unchangeable key, wherein said means for encrypting digitaldata using a changeable key and said means for encrypting said digitaldata using an unchangeable key are capable of producing double encrypteddigital data, and wherein said unchangeable key is capable of beingoperationally unchangeable at least during said encrypting of saiddigital data.
 185. The apparatus according to claim 184, wherein saidmeans for encrypting digital data using said changeable key comprisesmeans for encrypting said digital data prior to said means forencrypting said digital data using said unchangeable key.
 186. Theapparatus of claim 184, wherein said means for encrypting digital datausing said unchangeable key comprises means for encrypting said digitaldata prior to said means for encrypting said digital data using saidchangeable key.
 187. The apparatus of claim 184, wherein said means forencrypting digital data using said changeable key and said means forencrypting said digital data using said unchangeable key comprise meansfor encrypting said digital data prior to storing, copying and/ortransferring said double encrypted digital data.
 188. The apparatusaccording to claim 184, wherein said means for encrypting said digitaldata prior to storing, copying and/or transferring said double encrypteddigital data is executed in priority over one or more other tasks toprevent non-encrypted digital data from being stored, copied and/ortransferred.
 189. The apparatus according to claim 188, wherein saidchangeable key is supplied externally from said device.
 190. An articlecomprising: a storage medium having stored thereon instructions, that,if executed, result in: encrypting digital data using a changeable keyand an unchangeable key to produce double encrypted digital data,wherein said unchangeable key is capable of being operationallyunchangeable at least during said encrypting of said digital data. 191.The article according to claim 190, wherein said encrypting digital datausing said changeable key is done prior to said encrypting digital datausing said unchangeable key.
 192. The article of claim 190, wherein saidencrypting digital data using said unchangeable key is done prior tosaid encrypting digital data using said changeable key.
 193. The articleaccording to claim 190, wherein said encrypting of said digital data isdone prior to storing, copying and/or transferring said double encrypteddigital data.
 194. The article according to claim 193, wherein saidencrypting of said digital data prior to storing, copying and/ortransferring said double encrypted digital data is executed in priorityover one or more other tasks to prevent non-encrypted digital data frombeing stored, copied and/or transferred.
 195. A system, comprising: adisplay, said display capable of displaying digital data; a changeablekey encryption unit, said changeable key encryption unit capable ofencrypting said digital data using a changeable key; an unchangeable keyencryption unit, said unchangeable key encryption unit capable ofencrypting said digital data using an unchangeable key, wherein saidchangeable key encryption unit and said unchangeable key encryption unitare capable of producing double encrypted digital data, and wherein saidunchangeable key is capable of being operationally unchangeable at leastduring said encrypting of said digital data; and a storage medium, saidstorage medium capable of storing said double encrypted digital data.196. The apparatus according to claim 195, wherein said changeable keyencryption unit is capable of encrypting said digital data prior to saidunchangeable key encryption unit.
 197. The apparatus according to claim195, wherein said unchangeable key encryption unit is capable ofencrypting said digital data prior to said changeable key encryptionunit.
 198. The apparatus according to claim 195, wherein said changeablekey encryption unit and said unchangeable key encryption unit arecapable of encrypting said digital data prior to storing, copying and/ortransferring said double encrypted digital data.
 199. The apparatusaccording to claim 198, wherein said encrypting of said digital dataprior to storing, copying and/or transferring said double encrypteddigital data is executed in priority over one or more other tasks toprevent non-encrypted digital data from being stored, copied and/ortransferred.